Implementation of multi-energy balance (MEB) into SURFEX Patrick Samuelsson Stefan Gollvik SMHI Aaron Boone Christophe Canac Meteo France

No explicit canopy vegetation energy balance (temperature)! Current SURFEX ISBA Tn 3-L CRO Tg EBA D95 Tg No explicit canopy vegetation energy balance (temperature)!

We want to model this!

Snow well below the canopy Snow partly buries the canopy Multi-Energy Balance (MEB) Snow buries the canopy Snow well below the canopy Snow partly buries the canopy Tc Tv Tn Tg Tc Tv Tn Tg Tc Tv Tn Tg MEB is designed to work with snow schemes 3-L and CRO (requires separate snow energy balance) soil schemes 2-L & 3-L (force restore) and DIF (diffusion)

A SURFEX grid box PARK (wetlands) EVER (evergreen broadleaved forest) Towns Nature (bare soil/ vegetation) Lakes Sea/Oceans Snow occurs separately in each tile and each patch. Thus, for the nature tile we can have up to 12 separate prognostic snow storages. MEB is designed to work for all vegetated patches. A logical vector in namelist is used to decide for which patches MEB should be used. PARK (wetlands) EVER (evergreen broadleaved forest) TROG (tropical /C4 grassland) CONI (evergreen needleleaved forest) GRAS (temperate /C3 grassland) TREE (deciduous broadleaved forest) IRR (irrigated crops) SNOW (snow and ice) C4 (C4 crops) ROCK (bare rock) C3 (C3 crops) NO no vegetation

Motivations for MEB Canopy has low heat capacity (as top soil layer) but can only exchange heat via radiation and turbulent fluxes. Gives a relatively large and realistic diurnal cycle in canopy temperature. Gives a more physical consistent energy exchange between soil/snow and atmosphere. Replaces mulch-effect in present ISBA which parameterise presence of vegetation by decreasing heat transfer in upper soil. Tall canopy (low albedo) hides snow (high albedo). Important for snow evolution in forest areas  runoff and hydrology See radiation exchange on next slide… Enables interception of snow on canopy. Most important in low-latitude mountain areas where evaporation from intercepted snow can be ~30% of annual snow fall.

Radiation in MEB Short-wave radiation uses two reflections Low sun angle: SW radiation is absorbed mainly by the dark trees  Trees warm up  Gives Sensible heat to atmosphere LW radiation to surface which is absorbed by the “black snow” (ε~0.98)

Evaluation of MEB Two SnowMIP2 forest sites where snow interception matters Alptal (Switzerland), 1185 masl, trees: 25 m, LAI 4.2 Alptal (Switzerland), ISBA MEB Observed Snow depth at forest floor Fraser (US Rockies), 2820 masl, trees: 27 m, LAI 5 Fraser (US Rockies) ISBA MEB Observed Snow depth at forest floor Time over snow season

Low SW absorption by snow and low turbulent energy transfer Evaluation of MEB Two SnowMIP2 forest sites where snow interception matters Alptal (Switzerland), 1185 masl, trees: 25 m, LAI 4.2 Alptal (Switzerland), ISBA MEB Observed Snow depth at forest floor Low SW absorption by snow and low turbulent energy transfer Fraser (US Rockies), 2820 masl, trees: 27 m, LAI 5 Fraser (US Rockies) ISBA MEB Observed Snow depth at forest floor Time over snow season

Evaluation of MEB Sodankylä (Finland), 179 masl, trees: 12 m, LAI 1.2 Data via SRNWP Data Exchange Programme (see Andras’ talk Tuesday) Problems with quality of precipitation data (needs correction against daily SYNOP) MEB ISBA Observed July Jan Apr-May

Evaluation of MEB Sodankylä (Finland), 179 masl, trees: 12 m, LAI 1.2 ISBA Observed July January April - May Latent heat flux Sensible heat flux

Summary Multi-energy balance (MEB) parameterisation has been implemented in a test version based on SURFEX 6.1 code (isba.f90 and below). Work done, and more needed, to implement new physiographic data and variables in SURFEX code structure (above isba.f90). MEB is designed for all vegetated patches (forest to grass) but will probably be used mostly for forest patches. Will also become accessible from TEB. Not yet compatible with Canopy model. Extensive 0D testing with forcing from tower observations has just started. Will go on for a few months more. GOOD data is needed! MEB will be part of SURFEX X.X MEB in forest has been used for many years in SMHI regional climate model RCA and is now part of latest HIRLAM release. Thus “snow people” within HARMONIE has decided to head for SURFEX with MEB (forest) + 3-L snow + force-restore/DIF soil…

THANKS!